Because I'm lazy, I'll just refer to this post here where I mention three specific plugins to retool the mail() function. I can assure that all three work with WP3.0.X and I have just now tested the Shorten2Ping plugin as working perfectly with the ping.fm via the "secret email address" option, sent via SMTP (!) and not the always troublesome PHP mail() function.

In that same post I also mention - even though it's geared to one hosting company, it's generally true - that SMTP especially with SSL is highly recommendable to avoid soft-fails and message declines (or tarpitted) due to not using non-specific accounts. Set a "real" email account up on the same host as Shorten2Ping and send from it with SMTP and ping-fm will accept it perefectly.

Â¡Gracias don Samuel por un maravilloso plugin que nos viene de perlas!